The present invention pertains generally to a work vehicle that has a work implement connected to a movable boom assembly, such as a skid steer loader that has a loader bucket connected to a movable boom assembly. In particular, the work implement and movable boom assembly are hydraulically activated and share a common hydraulic circuit. The present invention relates to a work vehicle that includes an improved control system for controlling the work implement and the movable boom assembly in concert so that the common hydraulic circuit is optimally shared by the work implement and movable boom assembly. In this controlled manner, hydraulically activated movement of the work implement and the boom assembly is optimized using a single common hydraulic circuit.
Skid steer loaders are work vehicles that include four wheels rotatably mounted to a frame, an engine mounted on the frame and connected by a transmission to rotate at least two wheels, a cab compartment mounted on the frame that includes a seat for an operator, manual controls and a display panel disposed in the cab compartment, a boom assembly rotatably mounted on the frame and connected to a pair of hydraulic boom cylinders for moving the boom assembly, and an implement assembly connected to the boom assembly. Typically, one or more hydraulic cylinders are used to manipulate the implement assembly. Preferably, the implement assembly is a bucket assembly, wherein the implement is a loader bucket and a pair of hydraulic bucket cylinders is used to move the bucket assembly. Other types of work vehicles that are similar to skid steer loaders include tractors and bulldozers.
To operate the hydraulic boom cylinders and the hydraulic implement cylinders, an operator in the cab manipulates either hand or foot manual controls. The skid steer loader, or similar work vehicle, includes an electronic control circuit system that includes an onboard computer, microprocessor, or controller. For the purposes of this disclosure, a computer, microprocessor, or controller are considered to be equivalent and interchangeable elements. The onboard computer operates solenoids of electrohydraulic valves in a common hydraulic circuit that activates both the hydraulic boom and the hydraulic implement cylinders.
U.S. Patent Application Publication US 2001/0007087 A1 to Brandt et al., which is incorporated herein by reference for all it discloses, teaches a computer based control system for a skid steer loader that includes a computer receiving inputs from a control panel, various sensors, hand grip and foot pedal inputs, and a seat bar sensor. The computer generates outputs to hydraulic actuators and associated valves, and to electromechanical devices. Generally, movement of the hand grip and foot pedals generate hand grip and foot pedal inputs that are used by the computer to generate corresponding output signals directing activation of the hydraulic boom and hydraulic implement cylinders to effect movement of the implement assembly and the boom assembly.
The prior art work vehicles have certain drawbacks. First, to minimize space requirements, conserve materials and decrease costs, the hydraulic boom cylinders and the hydraulic implement cylinders are connected together in parallel into a common hydraulic circuit, thereby sharing a common hydraulic fluid supply and reservoir. Consequently, during operation of the work implement assembly and the boom assembly, hydraulic fluid from a hydraulic pump flows to each element in a parallel manner such that fluid flow divides and flows preferentially to the element having the least hydraulic resistance. Thus, there are times when certain movements stress the capacity of the common hydraulic circuit to provide sufficient hydraulic fluid to smoothly power simultaneous movement of the implement assembly and the boom assembly. For example, if the hydraulic sub-circuit activating the boom assembly is commanded by an operator to move very rapidly, most of the available hydraulic fluid will be diverted to the boom assembly leaving very little fluid available to the hydraulic sub-circuit for activating the implement assembly. Such is often the case when an operator directs the boom assembly to extend and lift the implement assembly while simultaneously directing the implement assembly to xe2x80x9cdumpxe2x80x9d the implement.
In this context, to xe2x80x9cdumpxe2x80x9d the implement merely means to rotate the implement, which is pivotally connected to one end of the boom assembly, towards the ground as shown by direction D in FIG. 1. The opposite of dumping the implement is to xe2x80x9ccurlxe2x80x9d the implement, meaning to rotate the implement away from the ground G in the direction C as shown in FIG. 5.
When dumping the implement, hydraulic implement cylinders are activated to extend respective pistons, which requires drawing hydraulic fluid from the common hydraulic circuit. If, at the same time the implement is dumping, the operator directs the boom assembly to rapidly extend, then the hydraulic boom cylinders are activated to extend their respective pistons, which also draw hydraulic fluid from the common hydraulic circuit. As described above, this simultaneous draw on the hydraulic fluid supply of the common hydraulic circuit sometimes results in an insufficient supply of hydraulic fluid to one of the parallel hydraulic sub-circuits. When the boom arm assembly extends while the implement dumps, it is the hydraulic sub-circuit activating the implement assembly that steals hydraulic fluid from the hydraulic sub-circuit activating the boom assembly in a manner that hinders optimal operation of the boom assembly.
On the other hand, an imbalance of hydraulic fluid sometimes occurs when the implement is curling while the boom assembly withdraws from an extended state to a retracted state. In this case, the hydraulic implement cylinders and the hydraulic boom cylinders are simultaneously retracting their respective pistons. Under these circumstances, the hydraulic sub-circuit activating the boom assembly generally acts to steal hydraulic fluid from the sub-circuit activating the implement assembly in a manner that hinders optimal operation of the implement assembly.
Thus, the prior art work vehicles, having a shared common hydraulic circuit for activating both the implement assembly and the boom assembly, have the drawback that activation of one of the hydraulically activated assemblies may compromise the optimal activation of the other hydraulically activated assembly.
Consequently, there is a need for a control system for controlling the activation of the hydraulic implement sub-circuit and the hydraulic boom sub-circuit of the common hydraulic circuit to ensure that hydraulic fluid is shared in a controlled or compensated manner so that neither hydraulic sub-circuit draws hydraulic fluid in a way detrimental to the other hydraulic sub-circuit. In other words, there is a need for a control circuit that automatically compensates for disproportionate fluid flow through two parallel hydraulic sub-circuits to ensure the proper operation of each sub-circuit and the corresponding assembly of the work vehicle it activates.
The present invention provides an improved electronic control system for a work vehicle, or like machine, having a boom assembly and a work implement assembly connected to the boom assembly so that the improved electronic control system of the present invention maintains the benefits of the prior art electronic control systems while overcoming the drawbacks of the prior art control systems.
Accordingly, an object of the present invention is to overcome the disadvantages of the prior art electronic control systems for work vehicles and other like machines.
Another object of the present invention is to provide an electronic control system for work vehicles, and like machines, that automatically compensates for disproportionate fluid flow through two parallel hydraulic sub-circuits to ensure the proper operation of each sub-circuit and the proper movement of the corresponding implement assembly or boom assembly of the work vehicle.
Another object of the present invention is to provide an electronic control system for work vehicles, and like machines, that automatically compensates for disproportionate fluid flow and is practical and cost effective to manufacture.
Another object of the present invention is to provide an electronic control system for work vehicles, and like machines, which automatically compensates for disproportionate fluid flow and is both durable and reliable.
In accordance with the above objectives, the first preferred machine embodiment of the present invention provides a work vehicle characterized by: (a) a frame; (b) a boom arm assembly connected at one end to the frame; (c) an implement assembly pivotally connected to another end of the boom arm assembly, wherein the implement assembly includes an implement; (d) a first hydraulic implement cylinder connected to the implement assembly and positioned to pivotally rotate the implement relative to the boom arm assembly when a piston of the first hydraulic implement cylinder is extended or retracted, wherein the first hydraulic implement cylinder is connected to a first electrohydraulic valve that activates extension and retraction of the piston of the first implement cylinder by directing hydraulic fluid to the first implement cylinder; (e) a second hydraulic boom cylinder connected to the boom arm assembly and positioned to move the boom arm assembly between a first retracted position and a second extended position when a piston of the second boom cylinder is retracted and extended, respectively, wherein the second hydraulic boom cylinder is connected to a second electrohydraulic valve that activates extension and retraction of the piston of the second hydraulic cylinder by directing hydraulic fluid to the second boom cylinder; (f) a common hydraulic circuit connected to provide hydraulic fluid to the first electrohydraulic valve and to the second electrohydraulic valve, wherein the first electrohydraulic valve is connected in parallel with the second electrohydraulic valve in the common hydraulic circuit; and (g) a controller connected to receive first input signals from a boom manual control sensor and second input signals from an implement manual control sensor, wherein the controller sends a first control signal to activate the first electrohydraulic valve in response to receiving a first input signal and the controller sends a second control signal to activate the second electrohydraulic valve in response to receiving a second input signal, wherein the controller is programmed to modify at least one of the first control signal and the second control signal in accordance with a table-based duty factor when the boom assembly and the implement are operated in a selected condition.
In accordance with a second preferred machine embodiment of the present invention, the first preferred machine embodiment is further modified so the first control signal is modified when the selected condition corresponds to dumping the implement while extending the boom arm assembly, wherein the modified first control signal effects a relative reduction in the hydraulic fluid flow from the first electrohydraulic valve to the first implement cylinder.
In accordance with a third preferred machine embodiment of the present invention, the first preferred machine embodiment is further modified so the second control signal is modified when the selected condition corresponds to curling the implement while retracting the boom arm assembly, wherein the modified second control signal effects a relative reduction in the hydraulic fluid flow from the second electrohydraulic valve to the second boom cylinder.
In accordance with a fourth preferred machine embodiment of the present invention, the second preferred machine embodiment is further modified so the second control signal is modified when the selected condition corresponds to curling the implement while retracting the boom arm assembly, wherein the modified second control signal effects a relative reduction in the hydraulic fluid flow from the second electrohydraulic valve to the second boom cylinder.
In accordance with a first preferred method embodiment of the present invention, a method of sharing hydraulic fluid for activating a boom arm assembly and an implement is characterized by the steps of: (a) inputting a first input signal from a first manual control sensor and a second input signal from a second manual control sensor to a controller connected to receive the first input signal and the second input signal; (b) sending a first control signal to control activation of a first electrohydraulic valve in response to inputting the first input signal into the controller; (d) sending a second control signal to control activation of a second electrohydraulic valve in response to inputting the second input signal into the controller, wherein activation of the first electrohydraulic valve directs hydraulic fluid flow through a first hydraulic sub-circuit and activation of the second electrohydraulic valve directs hydraulic fluid flow through a second hydraulic sub-circuit connected in parallel with the first hydraulic sub-circuit, and wherein hydraulic fluid flow through the first hydraulic sub-circuit effects movement of a boom arm assembly and hydraulic fluid flow through the second hydraulic sub-circuit effects movement of an implement; (e) determining whether the boom arm assembly and the implement are in a first condition, a second condition, a third condition or a fourth condition using the first input signal and the second input signal; (f) modifying at least one of the first control signal and the second control signal when the boom arm assembly and the implement are in the first condition or the second condition; and (g) controlling activation of the first electrohydraulic valve using the first control signal or a modified first control signal and controlling the activation of the second electrohydraulic valve using the second control signal or a modified second control signal, wherein the modified first control signal activates the first electrohydraulic valve to effect a relative reduction in hydraulic fluid flow through the first hydraulic sub-circuit and the modified second control signal activates the second electrohydraulic valve to effect a relative reduction in hydraulic fluid flow through the second hydraulic sub-circuit.
In accordance with a second preferred method embodiment of the present invention, the first preferred method embodiment is further modified so that the first control signal is modified when the first condition corresponds to dumping the implement while extending the boom arm assembly, wherein the modified first control signal effects a relative reduction in hydraulic fluid flow from the first electrohydraulic valve to a first implement cylinder.
In accordance with a third preferred method embodiment of the present invention, the first preferred method embodiment is further modified so that the second control signal is modified when the second condition corresponds to curling the implement while retracting the boom arm assembly, wherein the modified second control signal effects a relative reduction in hydraulic fluid flow from the second electrohydraulic valve to a second boom cylinder.
In accordance with a fourth preferred method embodiment of the present invention, the second preferred method embodiment is further modified so that the second control signal is modified when the second condition corresponds to curling the implement while retracting the boom arm assembly, wherein the modified second control signal effects a relative reduction in hydraulic fluid flow from the second electrohydraulic valve to a second boom cylinder.
Further objects, features and advantages of the present invention will become apparent from the Detailed Description of Preferred Embodiments, which follows, when considered together with the attached drawings.
FIG. 1 schematically illustrates a side view of the work vehicle in accordance with the present invention with the boom arm assembly extending while the implement is dumping (shown in phantom).
FIG. 2 schematically illustrates a side cut away view of manual controls in the cab of the work vehicle.
FIG. 3 schematically illustrates the common hydraulic circuit of the work vehicle shown in FIG. 1.
FIG. 4 schematically illustrates the control circuit of the work vehicle shown in FIG. 1.
FIG. 5 schematically illustrates a side view of the work vehicle in accordance with the present invention with the boom arm assembly retracting while the implement is curling.
FIG. 6 is a flow diagram of the method of sharing hydraulic fluid for activating a boom arm assembly and an implement in accordance with the present invention.